1. Field of the Invention
The present invention relates to a method for manufacturing an optical fiber array that comprises a plurality of bare fibers aligned and held at specific intervals and that facilitates the optical and mechanical coupling of the bare fibers and connection elements (for example, optical fiber lines, optical waveguides, optical elements, and other components on optical circuit boards) in a facing arrangement therewith, and more particularly to a method for manufacturing an optical fiber array aimed at eliminating the need to provide bare fiber guide members and reducing manufacturing costs without lowering the accuracy of the alignment intervals between the bare fibers.
2. Description of the Related Art
With such optical fiber arrays, the alignment intervals between the bare fibers can be set with high accuracy, and positional matching and optical coupling can be facilitated in relation to the optical fiber lines, optical waveguides, and the like on optical circuit boards arranged at corresponding alignment intervals.
Bare fiber guide members for accurately setting the alignment intervals between bare fibers are provided to conventional optical fiber arrays as the structural members of these optical fiber arrays. In conventional practice, the V-groove member a depicted in FIG. 25A, the capillary member b depicted in FIG. 26, and the like are known as such bare fiber guide members.
Specifically, the aforementioned V-groove member a is configured such that a plurality of grooves with generally V-shaped cross sections (V grooves) al are formed lengthwise on one of the surfaces thereof.
Bare fibers c are placed in the V grooves a1 of the aforementioned V-groove member a. The bare fibers c are secured in place by the two lateral inclined planes of the V grooves a1, and the fixing positions of these bare fibers c are set, by downward pressure from a presser plate d, as shown in FIG. 25B.
A plurality of bare fibers c can be aligned at regular intervals by forming a plurality of identically sized V grooves a1 at regular intervals. An optical fiber array e configured as shown in FIG. 25C is obtained by filling the gaps between the aforementioned bare fibers c (exposed fibers stripped of their outer envelopes, that is, fibers comprising a core and a cladding, are referred to as xe2x80x9cbare fibersxe2x80x9d; in a narrow sense, this term applies to exposed sections obtained by the stripping of the outer envelope from the area near the tip of a fiber ribbon), the V-groove member a, and the presser plate d with an adhesive and allowing this adhesive to solidify.
A capillary member b, on the other hand, is provided with a plurality of long and narrow holes b1 whose inside diameter is slightly greater (commonly about 1-2 xcexcm) than the outer contours of the bare fibers, as shown in FIG. 26. The fixing positions of the bare fibers are approximately set by inserting the bare fibers into the holes b1. The gaps between the bare fibers and the holes b1 are filled with an adhesive. The surface tension of this adhesive has an action whereby the bare fibers tend to be disposed roughly in the centers of the holes b1, and the bare fibers are fixed in the capillary member b by allowing the filled-in adhesive to solidify. The bare fibers and the wall surfaces of the holes b1 in the capillary member b are not necessarily in contact with each other due to the presence of the aforementioned adhesive, but because the surface tension of the filled-in adhesive has an action whereby the bare fibers tend to be disposed roughly in the centers of the holes b1 in the above-described manner, it is the wall surfaces of the holes b1 that set the fixing positions of the bare fibers. Consequently, a plurality of bare fibers can be aligned at regular intervals by forming a plurality of holes b1 whose centers are spaced at regular intervals.
It should be noted that the above-described V-groove member a, capillary member b, and other bare fiber guide members incur high manufacturing costs because these bare fiber guide members require high dimensional accuracy (commonly 1 xcexcm or less). Another drawback is that conventional optical fiber arrays are provided with the above-described bare fiber guide members as the structural members thereof, so the cost of such optical fiber arrays is proportionally higher.
To overcome this shortcoming, a method (see Japanese Unexamined Patent Application, (Japanese Patent Laid-Open No.07-168047) has been developed in which two tabular members f1 and f2 (see FIG. 27) with generally L-shaped cross sections are used instead of the above-described V-groove member a, capillary member b, or the like; bare fibers c are confined between these tabular members f1 and f2; and these bare fibers c are confined using an L-shaped ferrule with a generally L-shaped cross section and two flat plates parallel to two planes of this L-shaped ferrule.
This and other methods are disadvantageous, however, in that the alignment intervals between bare fibers cannot be set freely because these alignment intervals are determined by the diameters of the bare fibers. Another disadvantage is that when the diameters of the bare fibers vary as a result of dimensional nonuniformities, these nonuniformities accumulate and ultimately bring about marked variations in the fixing positions of the bare fibers in the areas near the two ends, making these methods unsuitable for reducing manufacturing costs without lowering the accuracy of the alignment intervals between the bare fibers.
By contrast, the bare fibers of optical fiber arrays provided with V-groove members a, capillary members b, and other bare fiber guide members are fixed individually, preventing the errors in the fixing positions from accumulating across a plurality of bare fibers.
A drawback, therefore, is that it is currently indispensable that the above-described V-groove members a, capillary members b, or other bare fiber guide members be provided in order to accurately set the alignment intervals between bare fibers, perpetuating the situation that prevents production of lower-cost optical fiber arrays.
With this technical background in view, a method for manufacturing an optical fiber array in which bare fibers can be aligned with high accuracy without the use of expensive bare fiber guide members has recently been proposed (see Japanese Patent Laid-Open No.06-11625).
Specifically, this manufacturing method entails installing a fiber-ribbon guide g, which is provided with a plurality of V grooves formed at an equal pitch in the upper surface thereof in the manner shown in FIG. 28A; a bare-fiber guide h (see FIG. 29), which is provided with a plurality of V grooves formed in the upper surface thereof; and a presser i, which is provided with trapezoid projections that fit into the V grooves of the aforementioned fiber-ribbon guide g. The tip portions of fiber ribbons k (exposed sections obtained by stripping away the jackets j1 of fiber optic cables j, that is, sections covered by ribbon material k1, are referred to as xe2x80x9cfiber ribbonsxe2x80x9d) are inserted into the V grooves of the aforementioned fiber-ribbon guide g to support these fiber ribbons k in a parallel formation; the tip portions of bare fibers m (in a narrow sense, xe2x80x9cbare fibersxe2x80x9d refers to exposed sections obtained by stripping the ribbon material k1 from the fiber ribbons k) are inserted into the V grooves of the aforementioned bare-fiber guide h to support the bare fibers m in a parallel formation; the aforementioned presser i is placed on the bare-fiber guide h to prevent the bare fibers m from shifting upward; and the external peripheral surfaces of the bare fibers m and fiber ribbons k are coated with an adhesive n.
According to this method, a bottom plate r (see FIG. 30) is then set such that a flat surface p is disposed underneath the bare fibers m in the manner shown in FIG. 28B and that an angular groove q is disposed underneath the fiber ribbons k; a top plate s (see FIG. 30) is set such that a flat surface p is disposed above the aforementioned bare fibers m and that an angular groove q is disposed above the fiber ribbons k; the aforementioned bare fibers m are sandwiched between the top plate s and the bottom plate r; the aforementioned adhesive n is allowed to harden in this state to bond the top plate s and the bottom plate r together; and the adhesive n and bare fibers m extending from the integrated top plate s and bottom plate r are removed, yielding an optical fiber array t such as that shown in FIG. 28C.
With this manufacturing method, the aforementioned bare fibers m are aligned with the aid of a fiber-ribbon guide g, a bare-fiber guide h, and a presser i, and the completed optical fiber array t is devoid of bare fiber guide members, making it possible to markedly lower the manufacturing costs of such optical fiber arrays.
This manufacturing method is disadvantageous, however, in that the bare fibers m cannot be accurately aligned for the reasons described below, and is thus similar to the method described in Japanese Patent Laid-Open No.07-168047 in its inability to serve as a method in which manufacturing costs can be lowered without reducing the accuracy of the alignment intervals between the bare fibers.
Specifically, it is possible to align with high accuracy the positions of the bare fibers m sandwiched between the bare-fiber guide h and the presser i in the manner shown in FIG. 28A (as shown in FIG. 28B, these positions correspond to the sections of the bare fibers m that extend from the integrated top plate s and bottom plate r, and are not incorporated into the optical fiber array because of being removed together with the exposed adhesive in the manner described above), but the bare fibers m gradually lose their tension in the direction from the bare-fiber guide h toward the fiber-ribbon guide g, making it difficult to align the bare fibers m at these positions with high accuracy. Applying tension to the bare fibers m between the fiber-ribbon guide g and the bare-fiber guide h has been suggested as a method for preventing the loosening of the bare fibers m, but this approach is disadvantageous in that it causes breakage of the bare fibers m.
In addition, applying the adhesive n to external peripheral surfaces of the aforementioned bare fibers m as shown in FIG. 28A causes the bare fibers m to move closer to each other as a result of the surface tension of the adhesive n, and when the top plate s or the bottom plate r is brought into contact from above or below with the bare fibers m coated with the adhesive n in the manner shown in FIG. 28B, the bare fibers m and the top plate s or the bottom plate r are brought closer to each other by the surface tension of the adhesive n. These phenomena cause the interval between the bare fibers m to vary, making accurate alignment of the bare fibers m difficult to achieve.
Furthermore, bringing the top plate s or the bottom plate r into contact from above or below with the bare fibers m coated with the adhesive n causes the bare fibers m to shift their positions by about 1 xcexcm due to slight differences in contact pressure on the bare fibers m between the top plate s and the bottom plate r, making accurate alignment of the bare fibers m difficult to achieve.
For these reasons, the method for manufacturing optical fiber arrays described in Japanese Patent Laid-Open No.06-11625 is disadvantageous in its inability to ensure accurate alignment of bare fibers m.
An object of the present invention, which was perfected in view of the above-described situation, is to provide a method for manufacturing an optical fiber array in which the alignment interval between the bare fibers can be set with high accuracy without the need to provide a bare fiber guide member.
Another object of the present invention is to provide a method for manufacturing an optical fiber array in which the alignment positions of the bare fibers do not change during the manufacturing step.
Yet another object of the present invention is to provide a method for manufacturing an optical fiber array in which the need to provide a bare fiber guide member is dispensed with and the manufacturing costs are markedly reduced.
Still another object of the present invention is to provide a method for manufacturing an optical fiber array whereby an optical fiber array whose bare fibers have high alignment density can be manufactured in a simple manner.
Specifically, the first manufacturing method of the present invention is a method for manufacturing an optical fiber array by providing a plurality of bare fibers aligned and held at specific intervals, and connecting these bare fibers to connection elements in a facing arrangement, comprising a step of aligning a plurality of bare fibers using a bare-fiber guide provided with a plurality of guide grooves formed in the longitudinal direction at specific intervals; a step of bringing the flat surface of an array body into contact with the bare fibers aligned by means of the bare-fiber guide, tacking the bare fibers onto the flat surface of the array body by direct or indirect bonding means while keeping the bare fibers sandwiched between the bare-fiber guide and the flat surface of the array body, and separating the bare fibers and the bare-fiber guide thereafter; and a step of forming a coating of uncured material on the external peripheral surfaces of the bare fibers tacked onto the flat surface of the array body and on the flat surface of the array body exposed between the bare fibers, curing this material, and bonding the bare fibers to the flat surface of the array body.
Furthermore, the second manufacturing method of the present invention is a method for manufacturing an optical fiber array by providing a plurality of bare fibers aligned and held at specific intervals, and connecting the bare fibers to connection elements in a facing arrangement, comprising a step of aligning a plurality of bare fibers using a bare-fiber guide provided with a plurality of guide grooves formed in the longitudinal direction at specific intervals; a step of bringing the flat surface of an array body or the flat member into contact with the bare fibers aligned by means of the bare-fiber guide, tacking the bare fibers onto the flat surface of the array body or the flat member by direct or indirect bonding means while keeping the bare fibers sandwiched between the bare-fiber guide and the flat surface of the array body or the flat member, and separating the bare fibers and the bare-fiber guide thereafter; a step of forming a coating of uncured material on the external peripheral surfaces of the bare fibers tacked onto the flat surface of the array body or the flat member and on the flat surface of the array body or the flat member exposed between the bare fibers, curing this material, and bonding the bare fibers to the flat surface of the array body or the flat member; and a step of superposing a flat member or the flat surface of an array body through the agency of an uncured material on the bare fibers bonded to the flat surface of the array body or the flat member, curing the material, and monolithically bonding the flat member and the flat surface of the array body.
Moreover, the third manufacturing method of the present invention is a method for manufacturing an optical fiber array by providing a plurality of bare fibers aligned and held at specific intervals, and connecting the bare fibers to connection elements in a facing arrangement, comprising a step of aligning a plurality of first bare fibers using a bare-fiber guide provided with a plurality of guide grooves formed in the longitudinal direction at specific intervals; a step of bringing the flat surface of a first array body into contact with the first bare fibers aligned by means of the bare-fiber guide, tacking the first bare fibers onto the flat surface of the first array body by direct or indirect bonding means while keeping the first bare fibers sandwiched between the bare-fiber guide and the flat surface of the first array body, and separating the first bare fibers and the bare-fiber guide thereafter; a step of forming a coating of uncured material on the external peripheral surfaces of the first bare fibers tacked onto the flat surface of the first array body and on the flat surface of the first array body exposed between the first bare fibers, curing this material, and bonding the first bare fibers to the flat surface of the first array body; a step of aligning a plurality of second bare fibers using the aforementioned bare-fiber guide or another bare-fiber guide of the same structure; a step of bringing the flat surface of a second array body into contact with the second bare fibers aligned by means of the bare-fiber guide, tacking the second bare fibers onto the flat surface of the second array body by direct or indirect bonding means while keeping the second bare fibers sandwiched between the bare-fiber guide and the flat surface of the second array body, and separating the second bare fibers and the bare-fiber guide thereafter; a step of forming a coating of uncured material on the external peripheral surfaces of the second bare fibers tacked onto the flat surface of the second array body and on the flat surface of the second array body exposed between the second bare fibers, curing this material, and bonding the second bare fibers to the flat surface of the second array body; and a step of superposing the first array body and the second array body through the agency of the uncured material such that the first bare fibers are disposed in central positions between the second bare fibers in the second array body and that the second bare fibers are disposed in central positions between the first bare fibers in the first array body, curing the material, and monolithically bonding the first array body and the second array body.